To Oscillator Screen Supply

Fig. Z I'M modulator.

"hanging around1' this fantastic learning spot, being educated in the true tradition of electronic repair. I was one jf the lucky ones, for I received the kind of electronic education that no school can ever hope to offer. I was taught "little tricks of the trade" thai have benefited me in later life — the type of education or which I will be eternally grateful

I built my very first transmitter under Jommie's tutelage, on the side portion of hK flLT1 shaped front counter. !i was far from state of the art for the time. With salvaged parts from an old Dumint TV set, circa 1952, it consisted of a 6AB4 oscillator multiplier driving a 6BQ6 final doublcr. Modulation was of the AM controlled carricr screen grid variety, using a 6SL7 speech amplifier and a 6SN7 control tube. A power transformer, 6AX5 rectifier, choke and a couple of filter caps made up the rest.

Oht I forgot to mention, Ihis was a VHP transmitter for six meters and amazingK enough it actually worked! Loading into a 11V Beam" TV antenna through 150 feet of twinlead, it reached Orlando, I lorida on its first contact — my very first contact!

Since thai time, I have continued to build whenever the bug hits me. Of late it tends to be in the realm of ^oiid state, but when the call wont out for tube type projects, I dug back through my files to see what 1 could come up with that would not only fill the bill but perhaps be an incentive to help repopulate six meters, a band that is all but deserted these days. What you see here is a basic design thai Larry Levy WA2INMand I camc up with back around 1964 or 1965. lit can be built with a number of different inexpensive tubes of the type commonly found in older tube-type TV sets, and in fact the entire transmitter less chassis can be salvaged from an old TV receiver. Just add your own enclosure, any fancy metering circuits you might desire, and package as you like. The only necessity is to follow good VMI construction technique, lly, keep all leads as short as possible and bypass everything to ground with .001 disc ceramic capacitors. If you want to make a little larger investment, substituting a type 2E26 or 6146 for the TV sweep tube in the final will provide ¡higher efficiency and greater power output for a given power input level. Depending upon supply voltage and final amplifier tube used, the transmitter can run up to 50 Watts power input AM or 65 Watts on FM or CW. AM modulation is accomplished by use ol a beam power tetrode connected as a choke-coupled heisrng modulator, and FM by re-connecting this modulator to screen-grid modulate the 8 MHz oscillator lube (crude but effective; this is a low cost project) and keying the final amplifier cathode foi CW. It's truly a "gut-level1' transmitter with k*w frills.

A type 6ESA6 telrude functions as an electron coupled oscillator at 8 Mil/, with the plate circuit: left broadly tuned through use of a 2.5 MHz choke ooil. A type 6AU6 will function equally well in this stage. The frequency multiplier is a type 6AQ5, though a 6CL6 will work better, and a 6BQ5 or 6CZ5 would also function quite admirably. The latter tube Eypes necessitate a 9 pin tube socket and an RCA Lube manual to determine pin connection. I his stage is a x3 multiplier to the area around 25 MHz, In turn, the 25 MH/ energy is coupled to the final amplifier tube of your choice, in this case a ralhcr inexpensive type 6DQ6B hori-

Loading into a "V Beam'' TV antenna through 150 feet of twmlead, it reached Orlando, Florida on its first contact - my very first contact!

crystal i 8mhï

6SA6 or 6au6

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DIY Battery Repair

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